In U.S. Pat. Nos. 3,652,076 and 3,665,815 issued to Edwin R. McIntier there is shown a jacket for applying pressure to the sides of the mold in which the sides of the jacket are of predetermined fixed length so that it is necessary to keep as many size jackets on hand as there are different sized molds. The jackets there shown comprise side members corresponding in number to the sides of the mold and pressureactuated devices at the corners of the side members of simultaneously moving all the side members to press each side member into engagement with its side of the mold. Structures of this kind, except that the side members are manually moved into engagement with the sides of the mold by lever means or by bolts, are shown in Mitchell, U.S. Pat. No. 2,903,777 and Beckman, U.S. Pat. No. 3,260,493. The jacket as herein disclosed is of the kind shown in the aforesaid patents, designed so as to accommodate molds of different size so that one such jacket is capable of use for a relatively large range of mold sizes, and so designed as to enable accommodating the jacket to a mold of predetermined size with very little effort. The jacket, as will be described, is relatively inexpensive to manufacture and is adapted to be lowered from a suspended position above the mold into a position of clamping engagement therewith and has for this purpose novel suspending tackle which holds the sides of the mold in downwardly divergent positions with respect to each other.